1. Field of the Invention
The invention relates to braking systems and, more particularly, relates to a spring applied, hydraulically released parking and emergency brake system which is usable with a vehicle such as a ride-on roller and which includes a manually actuated, self-resetting override valve that permits manual release of the brakes for the purposes of vehicle towing or the like. The invention additionally relates to a vehicle employing such a braking system and to a method of operating such a braking system.
2. Discussion of the Related Art
Many vehicles, and particularly many off-road vehicles, employ spring applied, hydraulically released (SAHR) parking and emergency braking systems. In these systems, a brake such as shoe assembly or a disk assembly is engaged under the force of a spring which permanently biases the brake towards its applied or engaged position. The brake is released by hydraulic pressure generated by a charge pump driven directly or indirectly by the vehicle's engine. In vehicles which either employ separate service and emergency braking systems or which lack a service braking system altogether, the emergency brake is released whenever the engine is operating and the charge pump is capable of generating hydraulic fluid pressure.
SAHR parking and emergency braking systems often include brake override assemblies to permit manual brake override for vehicle towing or assisted transport when the engine is not running, the charge pump fails, or when the vehicle otherwise is incapable transmitting hydraulic pressure to the brakes. One such brake override assembly is disclosed in U.S. Pat. No. 4,195,716 to Wirt (the Wirt patent). The brake override assembly of the SAHR braking system disclosed in the Wirt patent includes a manual cut-off valve and a manual hydraulic pump. The cut-off valve is located in a conduit leading from the system's brake control mechanism to the brake release actuators. The pump is disposed in an auxiliary conduit fluidically coupled to the brake release actuators. To release the brakes for towing or assisted transport, the cut-off valve is closed, and the pump is actuated to pressurize the brake release actuators and, hence, to release the brakes.
In braking systems such as the one disclosed in the Wirt patent, the brake release actuator of each brake assembly remains separated from the vehicle's tank or reservoir for so long as the manual override valve is in its actuated or closed position. As a result, the brakes remain disengaged unless and until the override valve is manually reset to its normal operating position in which fluid may flow from the brake release actuators to the vehicle's reservoir or tank. If the operator fails to reset the override valve to its normal operating position upon vehicle restart, the brakes cannot be reapplied. Hence, the safety of the operator and/or bystanders could be compromised by inadvertent operation of the vehicle with the parking and emergency brakes in an override condition.